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Tube radio rectifier diode

jpatti75

jpatti75

Amazing I haven’t electrocuted myself, yet.
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I’m working on a cheap little 1960 Admiral Celestial tube radio (model YH601) just for fun. It’s nothing special, but if I work out some issues, it will hang out in my garage. I replaced all the caps (electrolytic and the connecting caps), which solved the hum and the unit sounds halfway decent for just having crappy CB quality speakers. This radio has a silicon rectifier diode (1S314) and a 47ohm 2W resistor wire serving as a fuse, I believe. The resistor wire has a fabric cover and I notice that it gets hot and smokes a little at times. Given I replaced all the caps, I’m curious if the silicon diode could be contributing to the smoking, and if so, what would be a good modern replacement for it? If the diode isn’t the culprit causing the smoking of the resistor wire, what else should I be looking for?

here are the specs on the diode: https://www.web-bcs.com/diode/dc/1s/1S314.php?lan=en&info=true

Appreciate any recommendations on this boring little radio.
JP
 
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A 1n4005 or higher would do fine, but unlikely that's the issue. If the diode were bad either you would have no plate voltage or it would be raw ac. No voltage and it wouldn't work, ac and it would hum really loud for a few seconds until the cap blew up.

Check the voltages against the schematics. Fair guess something is drawing too much current and that should show up in the voltage readings. Look around the output tube in particular.

Also worth making sure that resistor is on value. If it's way high it may be dissipating more power than it should
 
Thanks for the recommendations, Gadget. I’ll leave the diode and do the checks you suggest!

JP
 
Started with the resistor. I lifted one end and checked the value and it came in at 60.6 ohms, so almost 29% above the value. So, it seems like I need to replace that resistor at minimum. Given its role as a fuse, do I need to find another wire type resistor, or is another type acceptable?

Thanks!
JP
 
Hi Gadget,

Wanted to close the loop with you on this one. In addition to replacing the resistor, I found that I missed replacing a small 5uf electrolytic capacitor, which was testing way high. How I missed it, I have no idea. Also, the 12BA6 power tube pins seemed to need a bit of cleaning and di-oxidizing. After those items were addressed the radio is performing pretty darn well. The sound was a bit distorted before, but is much cleaner sounding now. Seemingly not the greatest tuner and it probably needs a realignment, but some of the stronger FM stations in my area sound pretty decent. For what will be a garage radio, I think it will work out nicely.

As usual, thanks for your guidance. I wish I had a fraction of your knowledge of this stuff!

JP
 
might be a bit out of alignment. usually distortion on FM is the detector not quite centered. If you happen to have an RF signal generator and a VTVM you can give it an alignment. A sweep alignment is the better mousetrap but honestly for this just a basic peak the transformers and zero the detector alignment ought to work just fine. Likely instructions for both in the Sams if you are working from that.

also weak tubes don't help any, though quite frankly some of the budget FM radios from back then just weren't all that great. Zenith tabletops are usually pretty good though. Also just series string hot chassis type stuff but they perform better than you'd think they should. They also usually had decent size speakers and sometimes a tweeter as well.
 
Thanks, Gadget. The tubes in this little guy all tested pretty well for Emissions, leakage, and Gm on my Sencore, but that 12BA6 is a bit touchy/microphonic. I might change it out at some point. I don’t have the gear for an alignment (yet!).

I have heard lots of good things about Zenith tabletops. Curious if those with a phono input might be able to handle a Bluetooth connection, since so few US radios circa early 60’s have a tape and/or AUX input? The German radios of the time period seem to have a lot more input options, but they seem to garner a pretty penny. Have wanted to find a cool little tabletop for our kitchen, but my wife wants a radio with Bluetooth to play stuff in her iTunes library.
 
if one has a phono input it would be for a ceramic, so line level. Should work fine with any source you care to plug into it.

You can also hack them without too much bother, but if its a hot chassis radio there are some safety concerns involved with the grounding. Basically to feed an input though, you break the connection at the top of the volume control and feed in your other signal at that point. If you want to be able to use radio or aux input it needs an on/on 2 position switch installed somewhere.
 
Thanks much, Gadget. Yep, I think I’ll look for a stereo radio with an existing phono input then.
 
jpatti75 said:
Curious if those with a phono input might be able to handle a Bluetooth connection, since so few US radios circa early 60’s have a tape and/or AUX input? Have wanted to find a cool little tabletop for our kitchen, but my wife wants a radio with Bluetooth to play stuff in her iTunes library.
Click to expand...

You can check out "Mister Radio" channel on youtube ; he adds a bluetooth input to pretty much every radio he restores -

 
He's doing it a slightly different way but it all comes out about the same. I learned that trick from an old book written when these things were current. It was intended as either an FM tuner or phono input but an input is an input. I think they did it with caps for isolation but the transformer is a better way.
 
Ha! Yeah, I got a good laugh out of that one, too.

I’ve got a nice Motorola console in the living room (and a Magnavox in the basement I don’t know what to do with), but I’m looking for something small for our kitchen. Plus, I won’t stop until I have a nice vintage music machine in every room. I’m lucky I have an understanding wife. :biggrin:
 
gadget73 said:
might be a bit out of alignment. usually distortion on FM is the detector not quite centered. If you happen to have an RF signal generator and a VTVM you can give it an alignment. A sweep alignment is the better mousetrap but honestly for this just a basic peak the transformers and zero the detector alignment ought to work just fine. Likely instructions for both in the Sams if you are working from that.

also weak tubes don't help any, though quite frankly some of the budget FM radios from back then just weren't all that great. Zenith tabletops are usually pretty good though. Also just series string hot chassis type stuff but they perform better than you'd think they should. They also usually had decent size speakers and sometimes a tweeter as well.
Click to expand...
Hi Gadget,

I wanted to revisit our exchange on this Admiral radio and the distortion. Replacing the fusible resistor and the one small electrolytic capacitor I missed made a big difference in this radio. I also checked the voltage readings on the output tube and the were pretty close to spec, if anything just a little low by a few volts. I also connected it to my roof antenna to help get the best signal I can. While it is much improved, what I notice is that when I first turn the radio on I can pretty clean sound, but as it runs for about 5 minutes, the sound starts to distort a bit. Do you think this is indicative of alignment issues, or could the power and or output tube be faulty and the issue becomes more pronounced as they heat up?

Appreciate your thoughts (or anyone else who might have ideas) on these symptoms.

Thanks,
JP
 
could be components drifting and causing issues. Not sure if ifs components in the tuner section tweaking it a bit out of alignment, or something in the audio stage going funny though. Is AM clean when it starts to distort? That would rule out the audio section.
 
The AM is lousy, I can barely tune in a station to even tell if the sound is distorted. However, there are few stations even broadcasting in my area and the couple that are have a pretty weak signal. This radio has a small ferrite rod for an AM antenna. The AM mainly just sounds like a medium pitched frequency “buzz” for lack of a better description.
 
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